The presence of a sample in the neutron field of a nuclear reactor creates a perturbation of the local neutron fluxes. In general, the interpretation of the sample activation due to thermal and epithermal neutrons requires the knowledge of two corrective parameters: the thermal neutron self-shielding factor, Gth, and the resonance neutron self-shielding factor, Gres. Thermal neutron self-shielding factors in different materials (Al, Au, Cd, Co, Cu, Eu, Gd, In, Ir, Mo, Ni, Pt, Pb, Rh, Sc, Sm and Ta) and different geometries (foils, wires, spheres and) have been calculated by using the MCNP code.

Nuclear Instruments and Methods

The exchange biasing field (Heb) and coercive field (Hc) of molecular‐beam‐epitaxy‐grown Cu/Ni80Fe20/Fe50Mn50 samples in [111], [001], and [110] orientations have been investigated by longitudinal Kerr effect measurements. Ni80Fe20 and Fe50Mn50 were deposited as orthogonal wedge‐shaped layers on single‐crystal Cu substrates in a magnetic field, enabling the study of the thickness dependence of Heb and Hc on a single sample for each orientation. A strong dependence of Heb and Hc on the growth orientation is observed. The results are interpreted in terms of the observed noncollinear spin structure of the antiferromagnet and a comparison is given with the predictions from recent theoretical models.

Orientational dependence of the exchange biasing in molecular‐beam‐epitaxy‐grown Ni80Fe20/Fe50Mn50 bilayers (invited)

Ministry of Industry of Turkey, SANTEZ project number 00058.STZ.2007-1; TUBITAK project number 107T117

/pdf/high-quality-ito-thin-films-grown-by-dc-and-rf-sputtering-12mu4h326k.pdf

High quality ITO thin films grown by dc and RF sputtering without oxygen

Kesterite Cu2 ZnSnS4 is a promising photovoltaic material containing low-cost, earth-abundant, and stable semiconductor elements. However, the highest power conversion efficiency of thin-film solar cells based on Cu2 ZnSnS4 is only about 11% due to low open-circuit voltage and fill factor mainly caused by antisite defects and unfavorable heterojunction interface. In this work, a postannealing procedure is proposed to complete a Cd-alloyed Cu2 ZnSnS4 device. The postannealing to complete the device significantly enhances the performance of the indium tin oxide and promotes the moderate interdiffusion of elements between the layers in the device. As a result of the diffusion of Cu, Zn, In, and Sn, the interfacial electron and hole densities are improved, leading to the achievement of a suitable band alignment for carrier transport. The postannealing also reduces the interface traps and deep-level defects, contributing to decreased nonradiative recombination. Therefore, the open-circuit voltage and fill factor are both improved, and an efficiency over 12% for pure sulfide-based kesterite thin-film solar cells is obtained.

Device Postannealing Enabling over 12% Efficient Solution‐Processed Cu 2 ZnSnS 4 Solar Cells with Cd 2+ Substitution

Spin currents have an important role in many proposed spintronic devices, as they govern the switching process of magnetic bits in random access memories or drive domain wall motion in magnetic shift registers. The generation of these spin currents has to be fast and energy efficient for realization of these envisioned devices. Recently it has been shown that femtosecond pulsed-laser excitation of thin magnetic films creates intense and ultrafast spin currents. Here we utilize this method to change the orientation of the magnetization in a magnetic bilayer by spin-transfer torque on sub-picosecond timescales. By analysing the dynamics of the magnetic bilayer after laser excitation, the rich physics governing ultrafast spin-transfer torque are elucidated opening up new pathways to ultrafast magnetization reversal, but also providing a new method to quantify optically induced spin currents generated on femtosecond timescales.

/pdf/ultrafast-spin-transfer-torque-driven-by-femtosecond-pulsed-4x8q4h872l.pdf

Ultrafast spin-transfer torque driven by femtosecond pulsed-laser excitation.

The structural, electrical and optical properties of RF sputtered In2O3?:?Sn (ITO) thin films and the effect of post-deposition annealing have been studied. The thickness ranges from 225 to 862?nm. X-ray diffraction, scanning electron microscopy (SEM) and atomic force microscopy (AFM) experiments were performed to study the structure and the surface morphology of these samples. We found that thinner films have a 100 texture and as the film grows the preferred orientation changes from 100 to 111. The lattice parameters are found to be larger than the bulk value, indicating that the samples are under a tensile stress. The grain size increases with increasing thickness. SEM images show a dense granular structure with grains having different shapes and sizes. From AFM images, the average surface roughness (rms) was estimated to be 3.89?nm. The energy gap was found to decrease from 3.65 to 3.50?eV as t increases from 225 to 866?nm. Annealing experiments were done, in the air, at temperature T in the 100?500??C range. We found that the 111 texture becomes stronger after the annealing treatment. A large increase of the grain size with increasing T is observed. The lattice constant decreases with T to become closer to the bulk value, i.e. annealing seems to relieve the stress present in the as-deposited films; T = 400??C seems to be the best temperature to obtain practically a stress free sample. We observe a large decrease in the electrical resistivity ? after annealing. The lowest ? value (16 ? 10?4???cm) was noted in the 699?nm thick sample annealed at 500??C. The decrease of ? seems to be the consequence of a larger grain size and a stronger 111 texture.

https://iopscience.iop.org/article/10.1088/0022-3727/39/1/027/pdf

Physical properties of RF sputtered ITO thin films and annealing effect

Ferromagnetic resonance in a coupled two-layer system

A series of Co thin films have been evaporated onto Si(100) and glass substrates. The Co thickness, tCo, ranges from 50 to 195 nm. The structural and magnetic properties have been investigated by x-ray diffraction, hysteresis curves, Brillouin light scattering and magnetic force microscopy (MFM) techniques. The Co thin films are found to be polycrystalline with (0001) texture. There is an increase of the grain size with increasing film thickness. The coercive fields range from values as low as 2 Oe in thinner films to the highest values, 2500 Oe, in 195 nm thick Co/Si films. The magnetocrystalline anisotropy field Ha decreases as the thickness increases; surface and stress induced anisotropies seem to contribute to the value of Ha. MFM images reveal a well-defined stripe pattern for thicker Co/Si samples. Such domains are not observed in the case of the thinner films. These so-called weak-stripe domains appear in magnetic films with a low or intermediate perpendicular anisotropy. Similar behaviour was observed in Co/glass samples, in addition, cross-tie walls were seen in thinner ones.

http://iopscience.iop.org/article/10.1088/0022-3727/37/18/014/pdf

A. Layadi

Papers

Physical properties of RF sputtered ITO thin films and annealing effect

Ferromagnetic resonance in a coupled two-layer system

Structural and magnetic properties of evaporated Co/Si(100) and Co/glass thin films

Effect of oxygen partial pressure on the structural and optical properties of dc sputtered ITO thin films

X-ray diffraction, microstructure, Mössbauer and magnetization studies of nanostructured Fe50Ni50 alloy prepared by mechanical alloying